This is starting to sound like a bug. Which is odd as I have been through that bit 3 times and it was never anything other than straightforward… Try an earlier save (i.e one early on when you enter Harbor Town).

Another way would be the console here is a link: http://www.worldofrisen.de/english/article_273.htm (edit: you could dig around to find Doyle's id and spawn him in Costa's hotel and see if that works)